Evolutionary Perspectives on Sibship

PSYC 452

Domenico DeCaro

Natalia Gonzalez

Natasha Grabowsk

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Buss says, “Brothers & sisters impose unique adaptive problems & have done so recurrently throughout

human evolutionary history. First, a brother or a sister can be a major

social ally- after all, your siblings are related to you by 50 percent. But sibs, perhaps more than all other relatives,

are also major competitors for parental resources.” (240)

WHAT IS SIBSHIP?

Rohde, P.A, Atzwanger, K., Bitocskaya, M., Lampert, A., Mysterus, I., Sanchez-Andres, A., & Sulloway,

F.J. (2003). Perceived Parental Favoritism, Closeness to Kin, and the Rebel of the Family: The Effects of

Birth Order and Sex. Evolution and Human Behavior, 24, 261-276. doi:10.1016/S1090-5138(03)00033-3.

Ross, J. & Austin, A. (Writer), & Calabrese, C.N. (Director). (2011). Competing for the Title [Television series episode]. In A. McLemore (Producer),

Dr. Phil. Los Angeles, CA: CBS Television Distribution.

SOURCES

BIRTH ORDER DIFFERENCES

• Birth order differences reflect differential parental care and/or sibling competition.

• In this study, measures of relationship quality within the family consists of:

• Parental favoritism

• Rejection of parental authority by becoming the rebel of the family

• Closeness to kin

• Seeking emotional support after distress

• Three determinants:

• Child’s reproductive value

• Child’s vulnerability & neediness

• Chances of future reproductive value

• For sibships of two, firstborns will feel closest to a parent.

• For siblings of three or more, middle-borns will feel least close to parents.

• Strength of these effects will be moderated by the mother’s reproductive value & her age.

• Although the mother should be the favored parent of all children, middle-borns will usually feel closer to the father or to a sibling.

• In regards to parental favoritism, middle-borns should be least favored.

• In sibships of three, middle-borns should be the most like to rebel.

PREDICTIONS

• Multinational convenience sample of university students

• Questionnaire - open ended answers, then arranged to a fixed option format

• Only participants born in the respective country are included

• Participants older than 30 were excluded

• Intact family environment when growing up was required

• Multiple regression

METHODS

RESULTS

• Birth Order & Perceived Parental Favoritism

• In sibships of two, 53% of the first-borns claimed their younger sibling was favored & 53% of the last-borns named themselves.

• First-borns & last-borns did not disagree that later-borns tend to be favored.

• In sibships of three, 35% of first-borns, 32% of middle-borns, & 49% of last-borns identified themselves as the favored child, disconfirming predictions.

•Birth Order & Rebelliousness Within Family

• In sibships of two, 53% of the first-borns claimed their younger sibling was favored & 53% of the last-borns named themselves.

• First-borns & last-borns did not disagree that later-borns tend to be favored.

• In sibships of three, 35% of first-borns, 32% of middle-borns, & 49% of last-borns identified themselves as the favored child, disconfirming predictions.

RESULTS

• Birth Order & Closeness to Kin & Non-kin

• In sibships of two, 53% of the first-borns named a parent as the closest person to them, compared to 45% of last-borns.

• In sibships of three or more, 52% of first-borns, 43% of middle-borns, & 47% of last-borns named a parent.

• 43% of middle-borns vs. 50% of non middle-borns name a parent.

•Birth Order & Mother’s Age at Participant’s Birth

• In sibships of three or more, 33% named their mother as the closest person.

• The quadratic birth order effect on closeness to mother was found among participants with older mothers.

• Effect results in lesser closeness with mother in middle-borns & greater closeness in non middle-borns.

RESULTS

• Rebelliousness & Closeness to Parents

• In sibships of two, 46% of those who called themselves the rebel chose a parent as the closest person vs. 60% of those self-designated non-rebels.

• This confirms the prediction that being the rebel of the family is connected with a lower level of family closeness.

•Emotional support after a distressing situation

• In sibships of two, there were no significant birth order differences in response to who the participant would call for emotional supports after a stressful experience.

• In sibships of three or more, 35% of last-borns named parents compared to 42% of first-borns & middle-borns.

DISCUSSIONFindings are important because they show that self-reports

regarding the status of rebellion are not only sibling stereotypes or personality differences, but instead are significantly correlated

with the emotional bonds within the family.

These results are similar to previous studies in that parents, especially mothers, are more responsive, verbal, & emotionally

expressive to the last-borns as opposed to the first-borns.

Findings are consistent with the idea that mothers with a low level of reproductive potential attempt to increase their maternal investment with the last-borns, increasing to the difference

between middle-borns & non middle-borns.

The distinction between first-borns & non first-borns that is used in the birth studies on personality may be misguiding.

The existence in the importance of the birth order effects limits the possibilities prenatal development processes create effects.

We have no evidence at the moment to link the quality of family relationships with the quality of prenatal environment. The

influences seem to act independent of one another.

CRITICAL REVIEW• Interesting Points

• The birth order differences have nothing to do with the personality differences found between siblings.

• Parents are more connected to those children who are last-born.

• The rebel child is typically the last-born member of the family, and is usually the one who feels the least close to their parents.

• Limitations

• Sample should consist of more than just college students.

• Study should assess the relationship between the birth order and other characteristics.

• Do these conclusions apply to those family which involve step-brothers, step-sisters, or step-parents?

• In sibships of three, which individual is typically the most spoiled and least connected with their parents?

• A. The last-born child

• B. The middle-born child

• C. The first-born child

• According to the video, what does Dr. Phil think?

• A. These situations are normal and therefore nothing can and should be done to change them.

• B. It is okay for siblings to tease like that.

• C. The first-born child should know better than to downsize a younger child.

• Which of these is not a measure of relationship quality within the family?

• A. Parental favoritism

• B. Personality differences between siblings

• C. Closeness to kin

TEST

QUESTIONS

A

C

B